Wolfgang Vizethum

Inducibility of drug-metabolizing enzymes in the rat skin

The influence of systemic application of chemically unrelated drugs and xenobiotics (phenobarbital (PB), rifampicin (Rifa), pregnenolone-16 alpha-carbonitrile (PCN) and 3-methylcholanthrene (MC) on drug metabolizing enzymes was investigated in the skin of rats of both sexes. The results were compared with those obtained in the liver. PB, Rifa and PCN induced the aryl hydrocarbon hydroxylase (AHH) in the skin though to a lesser extent than MC. The basal enzymic activity as well as the inducibility were considerably lower in the skin than in the liver. The activity of cytochrome c reductase was similar in all rats independently from the pretreatment. Only slight sex differences were noted: generally, the activity was higher in males. Cytochrome P-450 content of the skin could not be detected as well as various dealkylation activities.

Effects of Intravenous and Intracutaneous Bacillus Calmette-Guérin Application on the Drug-Metabolizing System of the Liver

Both single intravenous and repeated intracutaneous injections of bacillus Calmette-Guérin (BCG) resulted in alteration of the hepatic microsomal drug-metabolizing enzymes of the rat liver. The cytochrome P-450 content was not significantly altered; its activity (ethoxycoumarin O-dealkylation) was inhibited in both the intravenous and intracutaneous group. The arylhydrocarbon-hydroxylase and aminopyrine-demethylase activities were also diminished; decrease of cytochrome-c-reductase activity was noted after intravenous application only. Comparison of the results for the intravenous and intracutaneous application routes respectively showed qualitative and quantitative differences. The inhibitory effects of BCG treatment on the drug-metabolizing enzymes of the rat liver can only partly be explained by changes in the cytochrome P-450 system. These findings might lead to reconsideration of dosage of drugs in cancer (malignant melanoma) patients treated by combined chemoimmunotherapy.

Cutaneous cytochrome P-450 activity during hexachlorobenzene-induced experimental porphyria in rats.

The human population is exposed to a wide variety of insecticides, drugs, fungicides, and other environmental chemicals. Most of these xenobiotics are metabolized by membrane-bound, mixed function oxidases, which require NADPH/NADH and molecular oxygen. This oxidative metabolic step is mostly a hydroxylation, catalyzed by enzyme systems involving the CO-sensitive terminal monooxygenase cytochrome P-450. Cytochrome P-450 is a multicomponent group of mixed function oxidases which shows its highest activity in the endoplasmatic reticulum of the liver; however other tissues such as kidneys, small intestine, lungs, brain, lymphocytes and skin also contain these enzymes (Ullrich and Kremers, 1977). Cutaneous cytochrome P-450 may be of considerable interest in the biotransformation of potentially toxic chemicals of the environment. On the other hand, the oxidative metabolism of various drugs by the skin cytochrome P-450 may lead to the formation of reactive metabolites which are often carcinogens, mutagens or cytotoxic agents. In view of the biological importance of the skin cytochrome P-450, we found it of interest to determine its concentration and inducibility in rat skin microsomes during a long-time exposition to hexachlorobenzene (HCB). This chlorinated aromatic hydrocarbon is a world-wide distributed fungicide which has proved to be a potent inducer of the cytochrome P-450 in the liver of experimental animals (Stonard, 1975; Doss et al., 1976). Adult female Wistar rats (Zentralinstitut ftir Versuchstierzucht, Hannover, FRG), weighing about 200 g, were fed with a diet containing 0.05 % HCB over a period of 10 and 70 days, respectively. Wistar rats, kept under standard diet were used as controls. Ten and 70 days after the beginning of the HCB-application the animals were killed by decapitation and liver microsomes were prepared following the method of Kamath and Rubin (1972); liver microsomal cytochrome P-450 activity (expressed in terms of O-dealkylation of 7-ethoxycoumarin) was estimated using carbon monoxide, metyrapone, tetrahydrofurane and naphthoflavone as inhibitors (UU-

Einfluß von Chloroquin auf die Hexachlorbenzol-induzierte Porphyrie

SummaryRats were fed with a diet containing hexachlorobenzene (HCB) for about 60 days. At this time the porphyria was manifest as shown by significantly elevated porphyrins. Thereafter, chloroquine (CQ) was additionally given over a period of at least 6 weeks. At the end of the experiment the urinary porphyrin excretion and the porphyrin content in liver and skin were diminished in HCB-CQ-treated animals by about 50% compared to the HCB controls. The relative porphyrin distribution pattern was not influenced by CQ. In a further investigation the prophylactic effect of CQ could be demonstrated. Rats given CQ simultanously from the beginning of the HCB feeding showed a significantly delayed onset of porphyria.It is concluded from our results that CQ does not only form complexes with porphyrins during the treatment of the HCB porphyria. We rather assume an effect of CQ on the metabolism of iron.ZusammenfassungBei weiblichen Ratten wurde durch Applikation von 0,05% Hexachlorbenzol (HCB)-Futterzusatz eine Porphyrie erzeugt. Anschließend wurden die Tiere über maximal 6 Wochen zusätzlich mit Chloroquin (CQ) (50 mg/kg/Tag) behandelt und mit entsprechenden Kontrollgruppen verglichen.CQ bewirkte eine etwa 50%ige Senkung der Porphyrinausscheidung im Urin und des Porphyringehaltes in Leber und Haut gegenüber HCB-Kontrollen. Das relative Porphyrinverteilungsmuster wurde durch CQ nicht beeinflußt.In einem weiteren Experiment erhielten Ratten von Versuchsbeginn an simultane Gaben von CQ und HCB. Die CQ-Prophylaxe bewirkte eine signifikant verzögerte Porphyriemanifestation.Auf Grund der Ergebnisse schließen wir, daß bei der HCB-bedingten Porphyrie der Ratte der Wirkmechanimus des CQ nicht nur auf der Bildung eliminierungsfähiger CQ-Porphyrin-Komplexe beruht. Es wird vielmehr angenommen, daß durch CQ eine Beeinflussung des Eisenstoffwechsels vorliegt, die die Porphyrinstoffwechselstörung abschwächt.Rats were fed with a diet containing hexachlorobenzene (HCB) for about 60 days. At this time the porphyria was manifst as shown by significantly elevated porphyrins. Thereafter, chloroquine (CQ) was additionally given over a period of at lest 6 weeks. At the end of the experiment the urinary porphyrin excretion and the porphyrin content in lijver and skin were diminished in HCB-CQ-treated animals by about 50% compared to the HCB controls. The relative porphyrin distribution pattern was not influenced by CQ. In a further investigation the prophylactic effect of CQ could be demonstrated. Rats given CQ simultaneously from the beginning of the HCB feeding showed a significantly delayed onset of porphyria. It is concluded from our results that CQ does not only form complexes with porphyrins during the treatment of th HCB porphyria. We rather assume an effect of CQ on the metabolism of iron.

Erythrocyte ?-Aminolevulinic acid dehydratase activity in porphyria cutanea tarda

The activity is defined as nmol 8-ALA consumed/min/1 erythrocytes. The difference between controls and PCT patients were not significant. Simon and Kiss used the method of Mitchell et al. [3] for determining the ALA-D activity. This is a proved method, too, but the enzymatic activity is calculated in whole blood in contrast to Berlin and Schallers method using the hematocrit for evaluation. A decrease of hematocrit in the course of phlebotomy treatment of porphyria cutanea tarda might lead to a decrease of ALA-D activity, which could be the reason for the diminuation of enzymatic activity in the patients of Simon and Kiss and thus for the different findings. Simon and Kiss furthermore did not find a correlation between urinary porphyrin excretion and especially of porphyrin precursors (ALA and porphobilinogen) and therefore a pathognomonic value of this investigation could not be demonstrated. According to the above cited results we assume that there is no significant alteration in the ALA-D activity in red cells of patients with porphyria cutanea tarda.